drm/i915: Deal with TMDS DFP clock limits

drm/i915: Deal with TMDS DFP clock limits

Use the new helpers to extract the TMDS clock limits from
the downstream facing port and check them in .mode_valid().

TODO: we should check these in .compute_config() too to eg.
determine if we can do deep color on the HDMI side or not

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200904115354.25336-12-ville.syrjala@linux.intel.com
Reviewed-by: Lyude Paul <lyude@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>